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The influence of solar and geomagnetic activities on electrical propulsion system of ultra-low orbit gravity satellite was evaluated for the current 25th solar cycle. The orbit simulation was carried out and the data of GOCE mission was analyzed. The variation of atmospheric drag was analyzed. The influence of solar activity on propellant consumption and the influence of geomagnetic storm on drag-free operation were obtained. The results show that the orbit altitude of the satellite in the low solar activity years can be reduced by about 20 km compared with that in the high solar activity years, which is conducive to improving the gravity signal intensity. Strong geomagnetic storms usually increase the drag by 30% to 90% at ultra-low orbit, so thrust margin is required for geomagnetic storms. Designer should ensure high specific impulse in thrust range of 10% to 70% of the maximum thrust. The life consideration of this range is important.

Oblique shock waves are unavoidable in a rectangular hypersonic inlet, leading to a non-uniform flow field. While a significant body of the literature exists regarding the shock train modeling in a uniform incoming flow condition, few efforts have focused on the shock train behavior considering the influence of the shock wave boundary layer interactions. A low-order dynamic model of the shock train has been constructed with the help of the free interaction theory and a 1-D analysis approach. Experimental and numerical investigations have been carried out to evaluate the low-order model. The results show that the model has the capability of qualitatively analyzing the shock train behavior. In the cases with incident shocks, the rapid forward movement of the shock train has been observed by experiment. Besides this phenomenon was also modeled using the low-order model. Schlieren images show that when the shock train approaches the interaction zone, its behavior is characterized by oscillation and then follows a rapid forward movement with a linear increasing backpressure at 2.7 Ma. This phenomenon is analyzed theoretically based on the free interaction theory. Meanwhile with the help of the direct numerical simulation results from some existing studies, the flow structures in the interaction region and the following boundary layer also provide the evidence. [ABSTRACT FROM AUTHOR]

By simulating the change process of the inventory of scientific papers according to a mathematical model of the publishing process, we find that publication delay would cause statistical error of the scientific paper output indicator, i.e. the quantity of published papers. Based on a simulation model and the average publication delay, we construct an optimization algorithm of the actual scientific paper output using a nonlinear least squares algorithm and validate its accuracy. To simplify the solution process, we propose an approximate algorithm of the actual scientific paper output indicator which would help science and technology managers practically deduce an approximation of the actual indicator. This has implications for strategy decision making and allocation of resources for science and technology research by policy makers. [ABSTRACT FROM AUTHOR]

This paper presents a novel method of multiscale association for analyzfng a turbogenerator accident having strange behaviors and serious consequence. Wave, index (WI) and credibility of sensor fault are proposed based on multiscale analysis of th$ recorded data, and then the associational degree of WI is used to detect sensor fault. In addition, mechanism models are built to verify that detection. Furthermore, maximum likelihood method and neural network are applied to estimate the confidence interval of the fault sensor and the true signal. The estimation has been used to clearly explain the cause of this accident. [ABSTRACT FROM AUTHOR]

It was found through the experiments made with an Aton-type Hall thruster that some of the propellant was ionized in the buffer chamber by “quick electrons.” This ionization is called “preionization” to discriminate it from the ionization in the discharge channel. The effect of preionization on low frequency oscillation was experimentally studied by changing the electric field intensity in the buffer chamber. The relationship between low frequency oscillation and preionization ratio was investigated through numerical simulation using a one-dimensional quasineutrality hydrodynamic model. The results obtained indicate that the amplitude of low frequency oscillation decreases as the preionization ratio increases. It was found through the analysis and numerical simulation of the physical process of low frequency oscillation that the positive feedback of electron density was the main cause of low frequency oscillation. The increase of preionization ratio decreases the amplitude of the feedback variation thereby reducing the amplitude of low frequency oscillation. [ABSTRACT FROM AUTHOR]

Instead of the slab channel model used in previous work, a cylindrical model representing the actual annular channel in Hall-type stationary plasma thrusters is introduced in this paper for the near wall conductivity (NWC) effect on the current profile. The electron dynamics process in the plasma, however, is still described by the same test particle method in current theories where electrons are randomly emitted into the plasma from the wall to simulate electron scattering on the insulating wall. Monte Carlo method is applied to solve the model. The numerical results show that the current density peaks due to NWC near the inner wall of the channel is different from that near the outer wall, a typical annular effect other than in the slab model where the two current peaks are the same, and the ratio of them is approximately the same as the ratio of the inner and outer radii. Besides, the integrated current in the thin layer near the wall grows linearly with the electric field and quadratically with the inversed magnetic field. The peak current profile shifts to the center of the annular channel as the magnetic field decreases. These simulation results are in accord with the experimental data. [ABSTRACT FROM AUTHOR]

A discharge channel with a chamfered wall not only has application in the design of modern Hall thrusters, but also exists where the channel wall is eroded, and so is a common status for these units. In this paper, the laws and mechanisms that govern the effect of the chamfered wall on the performance of a Hall thruster are investigated. By applying both experimental measurement and particle-in-cell simulation, it is determined that there is a moderate chamfer angle that can further improve the optimal performance obtained with a straight channel. This is because the chamfering of the wall near the channel exit can enhance ion acceleration and effectively reduce ion recombination on the wall, which is favorable to the promotion of the thrust and efficiency. However, the chamfer angle should not be too large; otherwise, both the density of the propellant gas and the distribution of the plasma potential in the channel are influenced, which is undesirable for efficient propellant utilization and beam concentration. Therefore, it is suggested that the chamfer shape of the channel wall is an important factor that must be carefully considered in the design of Hall thrusters. [ABSTRACT FROM AUTHOR]

This paper presents a method for measuring the plasma parameters of a Hall thruster plume based on image diagnostics. A digital camera obtains the plume image, and the RGB (red, green, blue) data extracted from the plume image are related to the light intensity information of different spectral lines. A photographic method for obtaining the electron temperature distribution in the Hall thruster plume is established by using RGB data based on the collisional-radiative (CR) model. The results from this photographic method were compared with published results from measurements made with a Langmuir probe and simulated results. The trends of the electron temperature distribution were similar to those results. The limitations and application of the photographic method, which could ensure that it is suitable for diagnosing the plasma parameters of the in-orbit Hall thruster plume, are also discussed. [ABSTRACT FROM AUTHOR]

Hall thruster has the advantages of simple structure, high specific impulse, high efficiency, and long service life, and so on. It is suitable for spacecraft attitude control, North and South position keeping, and other track tasks. The anode layer Hall thruster is a kind of Hall thruster. The thruster has a longer anode area and a relatively short discharge channel. In this paper, the effect of the channel length on the performance of the anode layer Hall thruster is simulated by the PIC simulation method. The simulation results show that the change of the channel length has significant effect on the plasma parameters, such as potential and plasma density and so on. The ionization region mainly concentrates at the hollow anode outlet position, and can gradually move toward the channel outlet as the channel length decreases. The collision between the ions and the wall increases with the channel length increasing. So the proper shortening of the channel length can increase the life of the thruster. Besides, the results show that there is a best choice of the channel length for obtaining the best performance. In this paper, thruster has the best performance under a channel length of 5 mm. [ABSTRACT FROM AUTHOR]

The cylindrical Hall thruster has the good prospect of serving as a miniaturized electric propulsion device. A 2D-3V particle-in-cell plus Monte Carlo (PIC-MCC) method is used to study the effect of the magnetic cusp on discharge characteristics of a cylindrical Hall thruster. The simulation results show that the main ionization region and the main potential drop of the thruster are located at the upstream of the discharge channel. When the magnetic cusp moves toward the anode side, the main ionization region is compressed and weakened, moving upstream correspondingly. The ionization near the cusp is enhanced, and the interaction between the plasma and the wall increases. The simulation results suggest that the magnetic cusp should be located near the channel exit. [ABSTRACT FROM AUTHOR]